Devices for producing motion from electric current, including motors, meters, and torquers, generally contain a stationary member designated the "stator" and a moving member designated the "rotor". The stationary stator and the rotating rotor may be provided by permanent magnets, electromagnets, or coils of wire. The electromagnet is generally a coil of wire wound in association with a high permeability material, such as iron, so that current flowing in the coil produces magnetic flux in the permeable medium.
Coils wound without cores or other integral magnetic material and intended for use as rotors are referred to as moving coil rotors or devices. Such coil windings are characterized by low inertia and are useful in meters if the coils are constrained to make only a portion of a revolution or in motors if the coil windings rotate continuously. For motor applications with continuous rotation, brushes and commutation are provided for current flow into and out of the moving coil rotor.
Alternately, the coil windings may be stationary, forming a stator while a permanent magnet is used for the rotor. The stator coil windings are separately energized or excited according to any of the established methods to provide rotating or moving magnetic fields which in turn produce the desired motion of the rotor. In that event no brushes are necessary. In motors, such an arrangement is known as a brushless dc motor and is characterized by long life due to the absence of brushes.
In conventional drive motors the stator coil windings are separate coils, separately wound and arranged typically in a circular array or other geometrical configuration according to the number of phases and number of poles of the dc motor. The stator coil windings may include many separate coils to achieve the desired smoothness of motion for uniform drive applications. Similarly, many separate coils, separately wound, are also required for stepper motor applications according to the desired level of refinement or discrimination of the step motion to be achieved. The separate coils are sequentially or selectively excited and energized by switching or commutation electronics, for example, on a printed circuit (PC) board in which case the coils may be mounted on the PC board resulting in a three dimensional structure of substantial depth and considerable complexity.
In each of these applications the coil winding, whether rotor or stator, is positioned relative to the air gap of a magnetic circuit and it is a general objective in dc motor and meter design to minimize the air gap in order to maximize available magnetic flux. The conventional coil winding configurations, generally cylindrical three dimensional structures with substantial depth, limit the extent to which the air gap can be minimized. The conventional coil windings for rotors and stators in dc motors do not have compact configuration. Furthermore, conventional stator and rotor windings are not spatially compatible with PC board switching or commutation electronics or for embedding in a PC board.